Semiconductor devices are widely used in various types of electronic products, consumer products, automobiles, integrated circuit cards, and the like. One feature of semiconductor devices which is important in many of these applications is the small size of a semiconductor device, which includes both the semiconductor die and the package in which it is housed. Keeping device dimensions as small as possible is not only important to single chip devices, but to multiple chip devices as well. However, there is a competing desire for additional I/O's which tends to increase the overall size of the semiconductor device or results in a device having a very fine lead pitch which makes it difficult for the end user to handle.
In addition to establishing a small device size, manufacturers are also driven to maintaining a low cost of manufacturing devices. A significant material cost in manufacturing a semiconductor device other than the semiconductor die is the leadframe. For many devices, a customized leadframe must be designed and manufactured for each semiconductor die which is both costly and time consuming.
Multiple chip semiconductor devices are gaining popularity because multiple chip devices significantly increase device packing density on a substrate, for example on a printed circuit (PC) board. However, one aspect which is slowing industry acceptance of multiple chip devices is prohibitive manufacturing costs. Many multiple chip devices utilize expensive ceramic substrates and employ additive thin-film processing on semiconductor die, processes which significantly increase manufacturing costs.
Resin encapsulated semiconductor devices are usually packaged by either one of two methods. In one method, a semiconductor die, or a plurality of die, is placed in a package which is then individually mounted on a circuit substrate. In an alternate method, a semiconductor die, or a plurality of die, is mounted directly on the circuit substrate and then is provided with a protective encapsulation structure. The first mentioned method has the advantages that the die is sealed in and protected by the package. The packaged device is easy to test, handle, and install and the encapsulating package provides the desired degree of protection against the environment. In contrast, the second described method in which the die is connected directly to the substrate minimizes the area required by the die and thus allows a very high substrate packing density. In this method, however, an unpackaged die is less easily handled, tested, and burned-in, and is more subject to undesirable effects of the environment.
In addition to mounting multiple semiconductor dice onto a substrate for increased packing density, board space can be saved by the vertical mounting of a semiconductor device. Vertical devices are attractive because they have a very narrow horizontal cross section, which permits a greater circuit board mounting density. A typical vertically mounted device is a zig-zag in line package (ZIP) wherein the leads exit through the lower edge of the package. A disadvantage to the ZIP is that it is a through-hole type of package, and the leads may become damaged or bent which would render the connection to the board unreliable. Another type of vertical device is a single in-line memory module (SIMM). A SIMM actually consists of a multiplicity of individually packaged devices mounted on a board that has edge connectors for plugging into a socket. A disadvantage of a SIMM board is its size due to the individual packages. A further disadvantage of a SIMM is the cost associated with the assembly process of packaging each semiconductor die separately.